1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having a plurality of laterally spaced ribs extending in a lengthwise direction.
2. Background Art
It is known to use V-belts in automobiles to drive various accessories from the engine crank shaft. Several belts may be independently driven by the crank shaft. In one exemplary engine construction, one belt drives an alternator and a blower, a separate belt drives a power steering unit, and a third belt drives cooling equipment.
There has been a trend to reduce the weight and size of cars to reduce fuel requirements. In many of these cars, a V-ribbed belt is used having a body with longitudinally extending, load carrying cords and a plurality of V-shaped ribs spaced laterally from each other and extending longitudinally on one of the inside and outside of the belt body. The other of the inside and outside of the belt body has one or two plies of rubber-impregnated canvas cloth thereon. The belt can be arranged in a serpentine configuration to cooperate with several accessory pulleys. The belt may be tensioned by an idler pulley which is pressed against the non-ribbed surface. This non-ribbed surface is also used to drive one or more accessories.
Generally, the non-ribbed surface does not have the power transmission capability of the ribbed surface. Frictional wearing of the non-ribbed or ribbed surface may result in a lowering of the belt tension, which could result in slippage. When this occurs, the belt may be incapable of positive power transmission under a heavy load.
To overcome this problem, it is known to use double V-ribbed belts wherein a plurality of laterally spaced and longitudinally extending ribs are provided on both the inside and outside of the belt body. Typically, the ribbed portions on the inside and outside of the belt have identical rib pitch, rib height, and rib shape. Load carrying cords are embedded in the belt body between the inner and outer ribs.
A double V-ribbed belt is commonly used in compact automobile engine compartments. These engines may generate sufficient heat in these smaller compartments that the belts are required to operate in a high temperature environment. It is known to use natural rubber, styrene-butadiene rubber, and chloroprene rubber for belts in this environment. However, these belts using these rubbers are prone to premature cracking. Typically, the cracking occurs in the compression layer of the belt with the rubber therein in a hardened state.
Research has been done to improve the heat resistance of chloroprene rubber. Some improvement has resulted from these efforts. However, the improvement has been limited and in many environments the performance of the improved chloroprene rubber is still inadequate.
Studies have also been undertaken to use, as an alternative, rubber such as chlorosulfonated polyethylene rubber, hydrogenated nitrile rubber, or fluoro rubber. With a main skeleton therein that is highly saturated or completely saturated, these rubbers have excellent heat resistance. Among these rubbers, it is known that chlorosulfonated polyethylene is comparable to chloroprene rubber in terms of dynamic fatigue properties, wear resistance, and oil resistance. However, chlorosulfonated polyethylene has diminished water resistance characteristics resulting from the effects of the vulcanization process, particularly with an acid receiving agent. Typically, oxides such as MgO and PbO have been used as the acid receiving agent for chlorosulfonated polyethylene.
However, when an acid receiving agent having a lead compound, such as PbO and Pb3O4 is used, while water resistance is improved, there arises a problem with respect to pollution and sanitation attributable to the lead.
When MgO is used as an acid receiving agent, the water resistance is significantly deteriorated by MgCl2 during the crosslinking reaction. The resulting rubber may not be suitable for use in a power transmission belt.
On the other hand, while it is possible to obtain a composition with good water resistance using an epoxy-type acid receiving agent other than the metal oxide, the resulting product has a bad odor, making it unpleasant to those handling the composition.
While power transmission belts, made as described above, may have significantly improved belt running life and excellent heat resistance under high temperature conditions compared with belts using chloroprene rubber, these belts may have an unacceptably low life in a low temperature environment, such as at xe2x88x9230xc2x0 C. or lower. This may be attributable to the fact that chlorosulfonated polyethylene rubber is formed by chlorosulfonated polyethylene and contains chlorine. The cohesive energy of chlorine is increased at a low temperature to cause hardening of the rubber. At low temperatures, the rubber may lack elasticity and be prone to cracking.
Ethylene-xcex1-olefin elastomers, such as ethylene-propylene rubber (EPR) and ethylene-propylene diene rubber (EPDM) are polymers having excellent heat resistance and cold resistance. These elastomers are also relatively inexpensive. However, these elastomers have a low resistance to oil and as such are not commonly used in applications where they will encounter oil. Since dry frictional V-ribbed belts are prone to slipping when exposed to a significant amount of oil, their transmission capability is deteriorated, making them generally impractical for this environment. However, use of these elastomers in a power transmission environment has been studied, as disclosed in Japanese Patent Laid-Open Hei 345948/1994.
Ethylene-propylene rubber has a relatively low tear strength, which is reduced even further by using a peroxide crosslinking system. As a result, the load carrying cords tend to pop out during operation. It is also difficult to effectively increase the degree of vulcanization in the rubber using a sulfur crosslinking system, so that abrasion may be significant during operation. Abrasion dust tends to accumulate at the base of the ribs, and may cause adhesive wear. This also potentially leads to a significant noise generation problem. While using EPDM with a large number of double bonds in the molecules may increase the degree of vulcanization and adhesive wear properties, it tends to lower heat resistance.
In one form, the invention is directed to a power transmission belt having a body with a length, an inside, an outside, and laterally spaced sides. The body has a bonding rubber layer in which elongate load carrying cords are embedded to extend lengthwise of the body. The body has a first layer on the inside of the bonding rubber layer in which a plurality of laterally spaced ribs are formed extending lengthwise of the body, and a second layer on the outside of the bonding rubber layer in which a plurality of laterally spaced ribs are formed extending lengthwise of the body. The bonding rubber layer has a sulfur-crosslinked rubber composition including an ethylene-xcex1-olefin elastomer. At least one of the first and second layers has a crosslinking product that is an organic peroxide-crosslinked rubber composition including an ethylene-xcex1-olefin elastomer.
In one form, the first and second layers both have a crosslinking product including an organic peroxide-crosslinked rubber composition with an ethylene-xcex1-olefin elastomer.
In one form, there is no reinforcing cloth on any of the inside, outside, or laterally spaced sides of the body.
The ethylene-xcex1-olefin elastomer in the first and second layers may be at least one of ethylene-propylene-diene monomer (EPDM) and ethylene-propylene rubber (EPR).
The diene monomer may be at least one of dicyclopentadiene, methylene norbornene, ethylidene norbornene, 1,4-hexadiene, and cyclooctadiene.
The organic peroxide may be at least one of dicumyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, benzoyl peroxide, 1,3-bis-(t-butyl-peroxyisopropyl) benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, 2,5-dimethyl-2,5-(benzoylperoxy)hexane, and 2,5-dimethyl-2,5-mono(t-butyl peroxy)hexane.
The organic peroxide may be used either alone or as a mixture within a range of 0.005 to 0.02 mol g per 100 g of ethylene-xcex1-olefin elastomer.
The belt may further include a crosslinking co-agent that is at least one of TIAC, TAC, 1,2-polybutadiene, metal salts of unsaturated carboxylic acids, oxims, guanizine, trimethylol propane trimethacrylate, ethylene glycol dimethacrylate, N,Nxe2x80x2-m-phenylene bismaleimide, and sulfur.
The belt may further include one of a) a reinforcing agent that is at least one of carbon black and silica, b) a filler that is at least one of calcium carbonate and talc, c) a plasticizer, d) a stabilizer, e) a processing aid, and f) a colorant.
The belt may further include short reinforcing fibers in at least one of the first and second layers.
A plurality of the short reinforcing fibers may protrude at the laterally spaced sides of the body.
The short reinforcing fibers may be at least one of nylon 6, nylon 66, polyester, cotton, aramid fibers, aramid fibers having aromatic nuclei in the molecular structure, and aramid fibers sold commercially under any of the trademarks CONEX(trademark), NOMEX(trademark), KEVLAR(trademark), TECHNORA(trademark); and TWARON(trademark).
In one form, the short reinforcing fibers have a length of 1-20 mm.
The short reinforcing fibers may be present in an amount of 1 to 30 parts by weight per 100 parts by weight of ethylene-xcex1-olefin elastomer.
In one form, at least one of the first and second layers is fiber-reinforced rubber in which an ethylene-xcex1-olefin elastomer is graft-bonded with short fibers having a diameter of no more than 1.0 xcexcm and present in an amount of 1 to 50 parts by weight per 100 parts by weight of ethylene-xcex1-olefin elastomer.
In one form, the short fibers have a diameter of from 0.05 to 0.08 xcexcm and are present in an amount of 5 to 25 parts by weight per 100 parts by weight of ethylene-xcex1-olefin elastomer.
In one form, a boundary between the short fibers and ethylene-xcex1-olefin elastomer is grafted using an adhesive that is at least one of a) a silane coupling agent that is at least one of vinyl tris (xcex2-methoxyethoxy) silane, vinyltriethoxy silane, and xcex3-methacryloxypropyl trimethoxy silane, b) a titanate coupling agent that is at least one of isopropyl triisostearoyl titanate and unsaturated carboxylic acid that is at least one of acrylic acid, methacrylic acid, and maleic acid, and c) a novolac type phenol resin.
The ethylene-xcex1-olefin elastomer in the bonding layer may be EPDM with an iodine value from 4 to 40.
The bonding rubber layer may further have at least one of a) a reinforcing agent that is at least one of carbon black and silica, b) a filler that is at least one of calcium carbonate and talc, c) a plasticizer, d) a stabilizer, e) a processing aid, and f) a colorant.
The bonding rubber layer may further have a plurality of short fibers embedded therein.
The sulfur in the bonding rubber layer may be present in an amount of 0.5 to 3.0 parts by weight per 100 parts by weight of ethylene-xcex1-olefin elastomer.
The load carrying cords may have fibers that are treated by applying a resorcinol-formalin latex (RFL) solution thereto.
The fibers of the load carrying cords may be pretreated with at least one of an epoxy and isocyanate compound before treating with RFL.
It is an object of the present invention to provide a power transmission belt having an adequate running life in both high and low temperature environments, even with the various rubber layers in the belt repetitively deformed in compression and tension.
It is also an object of the invention to provide a belt with good resistance to water and other environmental contaminants.